Beam-forming is a well-known technique in the field of wireless (e.g. radio) communication. It may, for example, be used for improving the signal-to-noise ratio (SNR) for a communication link by steering the transmitted energy in, or collecting the received energy from, a favorable direction. As referred to herein, beam-forming may conceptually be accomplished by any suitable known or future techniques, and applicable details of those techniques will not be elaborated on further.
One example area of application where beam-forming may be particularly beneficial is millimeter wave (mmW) communication, where antenna apertures are typically small. Successful millimeter wave communication may even rely on effective beam-forming to accomplish acceptable performance (e.g. sufficient link budget) in some scenarios. This may, for example, be due to that the free-space attenuation of the radio signals that is associated with the high carrier frequencies used for millimeter wave communication is higher than the free-space attenuation of radio signals for lower carrier frequencies. To this end, highly directive beam-forming (i.e. using narrowly directed beams—high beam-forming resolution—achieved e.g. by an antenna array having a large number of antenna elements) may be applied in typical millimeter wavelength communication situations. Thus, in a typical millimeter wave communication application, many different beam-forming configurations may be possible but only one (or a few) enable efficient communications.
With a large number of antenna elements and high beam-forming resolution, it is typically very challenging to determine the optimal (or even a sufficiently good) beam direction. Different techniques to solve this problem are available.
For example, WO 2013/086164 A1 discloses an example method for millimeter wave beam acquisition.
One example a technique for determining beam direction is beam-sweeping, where a signal (e.g. a beacon signal, such as a pilot signal or a sync signal) is transmitted sequentially in different directions (corresponding to applicable beam-forming possibilities) and a communication link may be established based on how the signal of the different transmission instances is received at a prospective receiving device.
One problem with beam-sweeping is that—especially with a large number of possible beam directions—it may take a long time to find an optimal (or even a good enough) beam direction. This may, in turn, lead to that the fraction of time allocated for the initial search of an applicable beam direction may be undesirably large.
Therefore, there is a need for methods and arrangements for efficient selection of a beam-forming alternative among a plurality of beam-forming alternatives.